1. Field of Invention
This invention relates to devices incorporating optical waveguide arrays and more specifically to high speed optical waveguide modulator arrays which control the phase and/or amplitude of a free-space wavefront for beamsteering and other functions.
2. Description of Prior Art
A satisfactory method for wide angle, far field variable deflection or steering of collimated or coherent optical beams at high speeds has remained an elusive goal. Such a technology has been recognized as attractive for applications such as optical interconnects, optical switching, displays and optical radar.
Although some limited steering action has been obtained using modifications of single diode laser structures, arrays such as passive phase modulator arrays will be required to obtain large synthetic apertures necessary for narrow far-field patterns. Individual element phase control is difficult to attain using conventional diode laser arrays. At the longer microwave wavelengths, phased antenna arrays have been exploited for synthetic radar deflection. However, at optical wavelengths progress has been impeded by the difficulty of spacing emitters sufficiently closely (such that d.sub.m .ltoreq..lambda., where d.sub.m is the minimum interelement spacing and .lambda. is the wavelength) to eliminate sidelobes in the far-field radiation pattern. Sidelobes which may be considered a form of noise, are undesirable because they (1) interfere with the ability to direct intense optical energy to a single target, (2) limit the non-redundant angular range, and (3) reduce the number of discretely addressable points. We have now found a design for a waveguide array wherein sidelobes can be dramatically suppressed.
Examples of previously proposed optical waveguide arrays for beam steering, e.g., semiconductor arrays, are described in U.S. Pat. Nos. 4,219,785, 4,360,921, 4,462,658, 3,959,794 and 3,954,323. Generally, the described devices utilize uniform array spacing which radiate undesirable sidelobes as discussed above in addition to the main propagation optical lobe.
In other prior art systems used to deflect or steer optical beams, e.g., systems responsive to an electrical signal, deflection has been limited either to very small deflection angles which limit the number of separated resoluable points or exhibit slow deflection rates.
It may also be noted that E. Kapon et al, in Applied Physics Letters 45, 200 (1984) described chirped arrays of diode lasers to achieve in-phase operation of the laser outputs. Such laser arrays do not permit both phase and amplitude control over each element as required for beam deflection.
The above mentioned problems are substantially eliminated by the present invention.